1. Field of the Invention
This invention relates to a cordless telephone apparatus, and particularly to a cordless telephone apparatus which has a pager which reports an incoming call from a parent device or a radio telephone.
2. Description of the Related Art
Conventionally, an apparatus of this type has a structure, for example, shown in FIG. 13 in which a parent device 1 is connected via a radio channel with a radio telephone 2 and also connected with a subscriber's line 3.
When the apparatus received a calling signal from the subscriber's line 3, it provides the control shown in a flowchart of FIG. 14. First, at the parent device 1, the calling signal is input via a hybrid circuit 4 to a calling signal detector (not shown) which then detects it and delivers its detection output to a control circuit 5. When the control circuit 5 receives this detection output, it determines that there is an incoming call (step 101) and sets a synthesizer 6 at the frequency of a control channel. The control circuit 5 indicates an empty communication channel and applies the incoming signal, inclusive of an identification signal ID, to a transmitter 7 to thereby cause the transmitter 7 set in the control channel to transmit the incoming signal via a transmission antenna 8 (step 102).
On the other hand, in the radio telephone 2, a synthesizer 10 is set at the frequency of the control channel. To save the battery, the synthesizer 10 and a receiver 11 are turned on for a time t1 (step 201), and then turned off for a time t2 (step 202), which is repeated. When the receiver 11 is on and receives the incoming signal via a reception antenna 12 (step 203), it delivers this signal to an identification signal detector 13 and a reception field detector 14. When the identification signal detector 13 identifies an identification (ID) signal contained in the incoming signal and the reception field detector 14 detects the presence of a reception field, the control circuit 15 turns on a transmitter 16 (step 204). The control circuit 15 applies a signal responsive to an incoming signal, inclusive of the ID signal, to the transmitter 16 to cause same to transmit the responsive signal via a transmission antenna 17 (step 205). Thereafter, the control circuit 15 switches the synthesizer 10 from the frequency of the control channel to the frequency of the telephonic communication channel (step 206). When the receiver 18 in the parent device 1 receives the responsive signal via its reception antenna 19, it delivers the responsive signal to the identification signal detector 20 and reception field detector 21. When the detector 21 detects a reception field (step 103), the control circuit 5 causes the transmission of the incoming signal from being stopped (step 104). When no reception field is detected at the step 103, the control circuit 5 causes the incoming signal to be transmitted repeatedly and when the number of transmissions reaches n (step 105), the control circuit 5 causes the transmission of the incoming signal to be stopped in order to avoid the unnecessary use of the control channel. If at this time the calling signal continues to be still transmitted (step 106), a sounder (not shown) of the parent device 1 is rung (step 107). On the other hand, when the identification signal detector 20 identifies the ID signal contained in the incoming signal (step 108), the control circuit switches the synthesizer 6 from the frequency of the control channel to the frequency of an empty telephonic communication channel (step 109). When no ID signal is identified at the step 108, the control circuit 5 waits until it fails to receive a calling signal from the telephone circuit 3 (step 110).
Then, the control circuit 5 delivers a bell ringing signal to the transmitter 7 set to the telephonic communication channel to cause the transmitter to transmit the bell ringing signal via the transmission antenna 8 (step 111). When the receiver 11 in the radio telephone 2 receives this signal via the reception antenna 12 (step 201), it delivers the signal to the control circuit 15 which, in response to this signal, rings a sounder 23 (step 208). At this time, the control circuit 15 determines whether or not the hook switch, not shown, is switched on (step 209), and if the hook switch is on, the control circuit 15 causes the transmitter 16 to transmit a signal indicative of the unhooking via the transmission antenna 17 (step 210). Thereafter, a radio telephone 2 is brought to a telephonic communication state (step 211), so that telephonic communication is possible over a telephone receiver 24 and a telephone transmitter 25. When the receiver 18 in the parent device 1 receives the unhooking signal via the reception antenna 19 (step 112), it delivers this signal to the control circuit 5 which, in response to this signal, causes the transmission of the bell ringing signal to be stopped (step 113). This causes the parent device 1 to be also put to a telephonic communication state (step 114).
In the cordless telephone apparatus, the telephonic communication channel has a wide baseband zone, for example, of 3 KHz, to permit vocal transmission and requires a high field strength, for example, of 40 dB uV/m or more to maintain high S/N. The service area for the cordless telephone apparatus, however, is limited to a relatively narrow range, for example, of 20 meters. Thus, when the radio telephone is outside the service area, it cannot receive a bell ringing signal transmitted via the telephonic communication channel even if there is the incoming signal, and cannot sometimes notice that it is being called. In order to avoid this, the transmission output power could be increased so as to expand the service area, which, however, would undesirably increase the current consumption at the radio telephone to shorten the battery life and easily interfere with other cordless telephone apparatuses. In order to reduce the current consumed when the radio telephone is waiting for an incoming signal, the power source of the radio telephone is switched off and the parent device rings a calling sound. When the radio telephone becomes distant from the parent device, however the user cannot hear the calling sound.
The radio telephone is usually too large and weighty to carry. The radio telephone could be miniaturized, which would, however, increase the cost as well as require miniaturization of the batteries used to thereby shorten the battery life. This requires the antenna to be miniaturized, which undesirably reduces the gain of the antenna and hence the service area.
As just described above, in the conventional cordless telephone apparatus, when there is an incoming signal or call at the radio telephone and the radio telephone is outside the service area for the telephonic communication channel, the radio telephone cannot receive a bell ringing signal, so that it cannot determine that it is being called. In addition, the radio telephone is large-sized and weighty, so that it is poorly suited for portability and is not functional.